Electrochemical behavior of ferrocene in ionic liquid media

Electrochemical studies of four organometallic redox couples as possible reference redox systems in 1-ethyl-3-methylimidazolium tetrafluoroborate

“…We are aware of the ongoing discussion on possible concentration dependence of the diffusion coefficient on the concentration of ferrocene in solution [22][23][24]. This area of research definitely needs additional studies since currently there are contradictory information available in the literature.…”

“…Concentration dependent diffusion coefficients for ferrocene ranging from 1.3 × 10 −7 to 6.8 × 10 −7 cm 2 s −1 were reported in 1-butyl-3-methylimidazolium tetrafluoroborate (BuMeImBF 4 ) [24]. Data for ferrocene in 1-butyl-3-methylimidazolium hexafluorophosphate (BuMeImPF 6 ) range from 7 × 10 −9 to 3 × 10 −8 cm 2 s −1 , depending on the ferrocene concentration and the electrochemical method used [23]. A diffusion coefficient of 3 × 10 −8 cm 2 s −1 was measured for ferrocene [10] and a diffusion coefficient of the cobaltocenium cation was Table 6 Diffusion coefficients, D, medium viscosities at 25 • C, Á, and D Á values for ferrocene in several ionic liquids and in acetonitrile.…”

Ferrocene as a Reference Redox Couple for Aprotic Ionic Liquids

“…A diffusion coefficient of 3 Â 10 À8 cm 2 s À1 for ferrocene in 1-butyl-3-methylimidazolium hexafluorophosphate was deduced from cyclic voltammetry fitting, assuming a heterogenous charge-transfer rate constant k ¼ 0.0025 cm s À1 and electron transfer coefficient of 0.5 [20]. In addition, there are papers , depending on the ferrocene concentration and the electrochemical method used [24]. However, a recent paper by Rogers et al [22] suggests that diffusion coefficients of both ferrocene and cobaltocene in a number of imidazolium-based ionic liquids do not depend on Fc or Cc þ concentration in the range of ca.…”

The Kinetics of Ferrocene Volatilisation from an Ionic Liquid

“…[13] As ILs are still relatively new materials, a number of fundamental parameters and techniques have not yet been developed for ionic liquid systems, such as well-defined reference electrodes. Therefore, there is currently a heavy reliance on in situ reference couples, such as cobaltocenium j cobaltocene, [1] TMPD j TMPD + · and Ag( 0 ) j Ag I , [14] as well as a significant number of iron-based compounds, [1,15,16] although the use of ferrocene j ferrocenium [1,4,5,7,8,[15][16][17][18][19][20] appears to be especially prevalent. It has previously been observed that placing ILs in vacuo or under a flow of inert gas can result in the volatilisation of dissolved Fc, [4,7,8] and this fact has been partially attributed [8] to discrepancies in the literature regarding diffusion coefficient values, D, and the erroneous assumption that D is strongly related to Fc concentration.…”